http://arthra.ugal.ro/handle/20.500.14043/25350 2026-04-07T18:54:09Z http://arthra.ugal.ro/handle/20.500.14043/25369 Structure Assessment by X-Ray Difractometry for Ceramic Materials used in Oral Prosthetic Systems Ursache, Maria; Armencia, Oana The paper presents a difractometric analysis on two types of ceramics nowadays available on the market and frequently used in restorative dentistry: InLine (IVOCLAR) and Hera-Ceram (HAEREUS KULZER). The diffractograms obtained by projecting the x-ray beam on the ceramic surface allowed establishing the structural characteristics that could influence the tribological behaviour of certain ceramic materials by determining the crystalline parameters and/or amorphous network and correlate the results to the wear coefficient values of the concerned materials. This non-destructive method that characterise materials’ structure establishes several correlations between the macroscopic properties and their atomic structure. THE ANNALS OF UNIVERSITY “DUNĂREA DE JOS“ OF GALATI FASCICLE VIII, 2009 (XV), ISSN 1221-4590 TRIBOLOGY 2009-01-01T00:00:00Z http://arthra.ugal.ro/handle/20.500.14043/25368 A Fast Numerical Method to Predict Elastic Fields Due to Eigenstrains in an Isotropic Half-Space PartII. Program Validation and Simulations Spânu, Sergiu; Dearn, Emanuel A fast algorithm to solve the inclusion problem for arbitrarily shaped eigenstrains is validated in this paper. Influence coefficients formulas and numerical predictions for elastic fields due to a spherical region of uniform dilatational strains are compared to existing analytical results. Numerical stress distributions when the eigenstrains vary proportionally to distance from the center of the sphere agree with the results obtained by Liu and Wang with a different algorithm. Residual stresses arising in an elastic-plastic non-conforming contact are also presented, suggesting that the region of plastic strains modifies the stress field induced by contact pressure by lowering its maximum intensity, thus making the resulting field more uniform THE ANNALS OF UNIVERSITY “DUNĂREA DE JOS“ OF GALATI FASCICLE VIII, 2009 (XV), ISSN 1221-4590, Issue 2 TRIBOLOGY 2009-01-01T00:00:00Z http://arthra.ugal.ro/handle/20.500.14043/25367 A Fast Numerical Method to Predict Elastic Fields due to Eigenstrains in an Isotropic Half-Space Part I: Algorithm Overview Spânu, Sergiu; Diaconescu, Emanuel A fast algorithm to predict elastic fields due to arbitrarily shaped eigenstrains in an elastic, isotropic half-space is advanced in this paper. The inclusion domain is partitioned in a set of cuboids of uniform eigenstrains, and solutions for each individual cuboid are superposed. These solutions, also known as the influence coefficients, are derived from a problem decomposition, following a method suggested by Chiu. Computation of inclusion problem solution in infinite space is accelerated by implementing three-dimensional spectral methods, in a hybrid convolutioncorrelation algorithm. Pressure-free surface condition is imposed with the aid of Boussinesq fundamental solutions and superposition principle. The newly proposed algorithm appears well adapted to numerical simulation of elastic-plastic contacts. THE ANNALS OF UNIVERSITY “DUNĂREA DE JOS“ OF GALATI FASCICLE VIII, 2009 (XV), ISSN 1221-4590, Issue 2 TRIBOLOGY 2009-01-01T00:00:00Z http://arthra.ugal.ro/handle/20.500.14043/25366 Sliding Indentation Behaviour of x 65 Hydrogenated Steel Grade Spânu, Constantin; Teletin, Claudiu; Crudu, Ion; Mereuță, Valentin The paper presents an experimental research on non-hydrogenated and hydrogenated X 65 steel samples. The steel was obtained from a continuous casting slab, this grade being used in petroleum industry. The hydrogen has an embrittlement action on the steel and reduces its mechanical properties. In time the hydrogen diffuses to the surface, so its concentration is higher into the superficial layer than the one into the material bulk. In the paper this action is appreciated by a sliding indentation test. It was found that low indentation forces generate smaller trace widths as the hydrogenation duration increase, due to the hydrogen into the superficial layer. For big indentation forces, the trace widths are bigger than the above ones caused by a lower hardness. The decrease of hardness is due to the lower hydrogen concentration in the bulk and the deeper extent of the plastic deformations. This aspect is confirmed by the value of a parameter defined in this paper THE ANNALS OF UNIVERSITY “DUNĂREA DE JOS“ OF GALATI FASCICLE VIII, 2009 (XV), ISSN 1221-4590, Issue 2 TRIBOLOGY 2009-01-01T00:00:00Z